1. Field of the Invention
The present invention relates to method of performing an area update for a terminal equipment in a communication network, and also to a correspondingly adapted terminal equipment.
2. Description of the Prior Art
Generally, communication networks consist of an access network and a core network. The access network is specifically adapted to a connection technology used for terminal equipment communicating with/via the network, whereas the core network is connection technology independent and manages the functions the network offers to the terminals registered in the network.
Currently, for example, there exists the GSM network (GSM=Global Standard for Mobile Communication), consisting of a so called base station subsystem BSS as the access network part and the core network comprising e.g. the mobile services switching center MSC, a home location register HLR, visitor location register VLR etc. The base station subsystem BSS is connected to the core network via an interface known as A-interface. Further, the base station subsystem comprises a plurality of base station BS and/or base transceiver stations BTS under control of a base station controller BSC. Each base station BS defines a cell and a plurality of cells form a location area. Typically, a location area has a size (number of cells) such that one MSC may effect control of communication within a location area. The above briefly described GSM communication system is also known as a second generation system (2G), which initially was basically intended and provisioned for speech data transmission (circuit switched data, real time data transmission).
Meanwhile, however, the need for packet data transmission (data different from speech) (non-real time, packet switched data) has increased, which led to the development of a so-called GPRS network (General Packet Radio Service). The GSM and GPRS communication network exist somewhat in parallel and rely on substantially the same access network. With regard to the core network, in a GPRS network the function of the MSC is performed by so-called GPRS Support Nodes GSN, among which there are Serving GPRS support nodes SGSN (and gateway GPRS support nodes GGSN). The BSS is connected to the SGSN via an interface known as Gb interface.
Hence, a single cell in such a communication network scenario may be connected to different core network elements of different types, i.e. SGSN and/or MSC/VLR.
Now, in case a terminal equipment (for example, mobile station MS) has moved within the network such that a new MSC/VLR and/or new SGSN is in charge for controlling communication in that part of the network, the necessity for a routing and/or location area update arises. The terminal then performs a routing and/or location area update, that is requests a new SGSN and/or MSC/VLR to take over communication control for the requesting terminal equipment. In such a routing and/or location area update RAU/LAU, the terminal equipment transmits the old, that is previous, routing area identity RAI and/or location area identity LAI of the routing/location area it was previous attached to and/or communicating with.
Using the transmitted RAI (LAI), the new core network element finds an address of the core network element previously in charge for controlling/managing communication with the terminal, that is the new core network element in the new routing area may locate the previous (old) core network element (SGSN and/or MSC/VLR) from where the subscriber data for the requesting terminal equipment are sent to the core network element at the new (current) location (new SGSN and/or new MSC/VLR).
With a continuously progressing development in communication networks, also a so-called third generation (3GPP=3rd generation partnership project) of communication networks is being developed. The communication network of the third generation is also referred to as UMTS (Universal Mobile Telecommunication System). According to UMTS/3GPP specifications, base stations in GSM correspond to Node_B's, mobile stations MS as terminal equipment are referred to as user equipment UE, etc. Also with a third generation (3G) communication network, a circuit switched data transfer (for example, for speech) as well as a packet switched data transfer is enabled. To this end, the 3G access network is connected or at least connectable via a lu-CS interface to a 3G MSC/VLR and via a lu-PS interface to a 3G SGSN.
With a demand that most recently developed equipment should be downward compatible, that is compatible to previously developed standardized systems, there will arise a situation, in which, for example, a 2G SGSN as well as a 3G SGSN are both connected to the same cell and/or location (routing) area of an access network.
For example, so-called GERAN cells enable the connection of 2G as well as of 3G core network elements (for example, 2G SGSN and 3G SGSN) to the same cell/location (routing) area. (GERAN=GSM EDGE Radio Access Network, EDGE=Enhanced Data rates for GSM Evolution). In case of SGSN's as an example for core network elements, a 2G SGSN is connected to a GERAN cell/routing area (that is to the GERAN access network) via the Gb interface, whereas a 3G SGSN is connected thereto via the lu-PS interface. Such a connection to a single GERAN cell/routing area of different core network elements of the same type (that is SGSN with lu-PS or Gb interface), is, however, required in 3G communication networks.
However, because a single routing area (or cell (as a smallest conceivable routing area)) can be connected to two different SGSN's, one with lu and other with Gb interface, the new SGSN receiving the terminal equipment's routing area update (RAU) request upon the detection of a necessity for routing area update does not know from which SGSN it should request the subscriber information associated with the requesting terminal, because the old routing area identifier RAI identifying the routing area in which the terminal equipment was previously present may indicate two different core network elements (i.e. 2G SGSN and 3G SGSN).
If, however, in the chosen example, a new SGSN does not know which previous SGSN to contact to retrieve the subscriber information of the requesting terminal equipment, a routing area update for a terminal equipment may fail and a call may be dropped.
Previously, in order to solve such a problem, it has been proposed to assign two separate routing area identities (RAI) to each routing area (and/or cell). However, assigning two identities inevitably doubles the address space for the routing areas, which is undesirable in terms of an additional need of network management in the core and access network. Also, the respective access network RAN (more specifically, the base stations and/or Node_B's) will have to broadcast two routing area identities for each routing area, while also terminals listening to the broadcasted information will have to be adapted to properly process and/or interpret the two broadcasted identities per routing area.
Thus, this previously proposed solution requires multiple changes to the existing communication network.
Document WO-A-00/21319 discloses the identification of a mobile station in a packet radio network. In this connection, the prior art document discloses that a temporary identity allocated to a mobile station by a core network element is allocated such that the network element encodes its own identifier, or part of it, into the temporary identity. The identity of the network element such as a SGSN node is assumed in this prior art to be derivable on the basis of the identities of the routing area served by the network element. However, as explained above, this assumption is no longer valid as a respective routing area is handled by several (different) network elements of the same network element type but of different core network types.
Therefore, the teaching as presented in WO-A-00/21319 can not be transferred to the present scenario in which it is required that a respective routing area has to be connectable to different core network elements of the same type.